Various types of polymer fine particles have been developed and used in a wide variety of fields. As the size of polymer fine particles decreases, they become easily aggregated. For the reason, polymer fine particles having a manageable size on the order of micron or more have been often used. However, with the recent progress in nanotechnology, new uses of small-size polymer fine particles have been developed. For example, for submicron-size fine particles within the wavelength of visible light, new uses have been developed taking advantage of optical characteristics such as dispersion and interference. Submicron fine particles are three-dimensionally closely packed to form a colloidal crystal and use of the colloidal crystal has been developed. To form such a colloidal crystal, monodispersed fine particles having a narrow particle size distribution are demanded.
On the other hand, among the polymer fine particles, a core-shell fine particle, in which not less than two types of polymers are combined, has attracted attention as a functional composite fine particle. The core-shell fine particle has a structure, which has a core layer (core fine particle) and a shell layer. The shell layer is formed of sufficiently dense polymer chains. One end of each of the polymer chains forming the shell layer is fixed on the surface of the core layer. Among the methods for producing a core-shell fine particle, in particular, one of the living radical polymerization methods, namely, atom transfer radical polymerization (ATRP), has recently attracted attention since a graft chain can be formed densely on the surface of a polymer fine particle. The graft chain densely provided also contributes to suppressing aggregation of a core-shell fine particle due to its sterical repulsion.
Patent Document 1 discloses a method for producing a core-shell fine particle by producing a fine particle containing an ATRP initiating group by precipitation-polymerization of a monomer having the ATRP initiating group with divinyl benzene in an organic solvent (acetonitrile solvent) and subsequently subjecting the produced fine particle to graft polymerization.    Patent Document 1: Japanese Laid-Open Patent Publication No. 2004-18556 (page 2, 4 and 5)